THE SECRETIONS. 



the mercuric salt has been added. Then there is produced a 

 vt'i-y characteristic yellow color, due to the precipitation of 

 nH'ivuric hydrate. On this reaction is based Liebig's method 

 for tin- (Teterrnlhation of urea. 



T. Place one cubic centimetre of a solution such as that used 

 in the last experiment, in a test-tube, and then fill the latter 

 exactly with a solution of sodium hypochlorite. Invert the 

 tube once or twice, and plunge it into a basin containing mer- 

 cury. A most vigorous evolution of gas takes place ; this con- 

 sists of nitrogen. 



The reaction which occurs is illustrated by the following 

 equation : 



The carbonic acid which is generated in the reaction is absorbed 

 by the solution of sodium hypochlorite. 



Instead of sodium hypochlorite, the similar salt of potassium 

 or calcium might be used in this experiment. 



** 186. Separation of uric acid (C 5 H 4 N 4 8 ) from 

 Urine. Place 200 cubic centimetres of urine in a narrow glass 

 cylinder, and add two or three cubic centimetres of pure nitric 

 acid. After twenty-four hours a brick colored or brown sedi- 

 ment will have subsided, which consists of crystals of urj&ajjid, 

 strongly tinted with the coloring matter of urine. These pre- 

 sent, under the microscope, the most various forms, the more 

 common being rhombic tables or columns and lozenge-shaped 

 ils ; the 3 7 ellow or brown color which such crystals pos- 

 sess is very characteristic of uric acid. 



Decant the urine from the red sediment of uric acid, which 

 may be freely washed with distilled water, as uric acid requires 

 14,000 times its weight of cold and 1800 times its weight of hot 

 water to dissolve it. The sediment may then be collected on 

 filtering paper and subjected to the following tests : 



1. Place a small quantity of the cr3 T stals on a microscopic 

 slide, and add a drop of liquor potassae. The crystals dissolve, 

 and a solution of urate of potassium is obtained (GjHjEL^Og). 

 Now add carefully an excess of nitric or hydrochloric acid, 

 when uric acid will be again obtained in the form of crystals, 

 which may be further examined. 



It may be well to state that uric acid often occurs as a de- 

 posit in urine which has not been artificially acidified, and that 

 the crystallographic characters of the substance are very various 

 and soim-t iim-s puzzling. The typical crystals of uric acid are 

 undoubtedly rhombic plates with extremely obtuse angles; the 

 typical form is, however, very frequently modified ; thus spin- 

 dfe-ehsped figures are formed by the rounding of the obtuse 

 angles, or the primary form is so modified that needles are- 

 formed which occur in groups (fig. 305). Not at all unfrequently 



